Hey i tried it but it is the same at the half point the directional light suddenly turn to negative.
i made a new blueprint with only sky atmosphere and a directional light an on the light with the property Forward Shading Priority on one, i changed nothing else.
then i just made a float with the range of 0 to 24 and the following components that fire from the constructor script :
when i put the blueprint in my scene and go to the 0 time:
then i see the directional light on 180 on the z rotation axis
then when i go to a half point like day of time 12:
the directional light suddenly goes to - 180 on the z axis :
very weird that this happens